Based on the chicks you are getting, I would expect both parents to be blue. Or maybe one blue parent and one black, with the blue chicks ranging in shade from dark to very light indeed.
Have you bred either of them with any other chickens in the past? If not, you might try it, as a test to see what you get. Maybe breed the rooster with something like a Barred Rock hen (should absolutely not have the Blue gene, but the chicks would be color-sexable Easter Eggers so someone might like to buy the pullets after you see what colors they are.)
If you have any lavenders, you could also test-mate to see if either the hen or the rooster are carrying lavender. For this purpose, "lavender" is any chicken of any breed that has the lavender gene (even if it's a Porcelain d'Uccle or an Isabella Brahma or a Lavender Orpington or something like that.)